Taking on Transcritical in Cold Storage

Pete Lepschat, engineering services manager for Hillsboro, Ore.-based Henningsen Cold Storage, has heard all of the “common folklore” about transcritical CO₂ refrigeration, such as that it uses a lot of energy.

So he was expecting to see an energy penalty when he commissioned a comparison between a transcritical system’s projected energy consumption and that of a low-charge central ammonia system.

But the transcritical CO₂ system turned out to be slightly more efficient and is expected to save 46,000 kWh/yr in electricity usage. “I was pleasantly surprised,” he said in a recent interview with R744.com.

Supported by the promising energy data and other metrics, the transcritical system has been running since June 20 at family-owned Henningsen’s new 111,000-sq-ft cold-storage facility in Grandview, Wash., supplying 187 TR of refrigeration capacity for a freezer (157 TR) and a dock area (30 TR).

This is the 95-year-old cold-storage operator’s first transcritical system, one of a small number of such systems being used in industrial refrigeration facilities in the U.S. Carnot Refrigeration supplied the system and PermaCold Engineering installed it.

Henningsen put the transcritical system (rack and condenser) on top of the dock roof, a small area that was relatively easy to support and offered more accessibility for forklifts.

The CO₂ system represents a bold departure for a cold-storage operator that has relied primarily on ammonia for decades. “It’s our first one, but I’m guardedly optimistic,” he said.

And last month, Henningsen installed a second transcritical system, from Hillphoenix, at an existing plant in Scranton, Pa. Henningsen also runs 10 central ammonia refrigeration plants (three with a low-charge configuration) and one leased facility using a synthetic refrigerant.

For the Grandview project Lepschat benefited from the advances transcritical refrigeration – more commonly employed in supermarkets– has made in the industrial sphere, particularly in Canada. “CO₂ is moving quickly in the market,” he said. “So there’s more information on it.”

Though hopeful, Lepschat understands that the jury is still out on the two new transcritical systems as he collects data on their energy performance, maintenance requirements and overall reliability in the demanding environment of a cold-storage plant. “It needs to be proven with real-life measures over the first year,” he said.

Lepchat, a highly regarded refrigeration engineer who has been with Henningsen for 24 years (and is on the board of RETA), started looking at transcritical systems seriously about 14 months ago as an option for the new Grandview plant. Prior to that, for another plant that opened last year in Salem, Ore., he was not quite ready to take on transcritical technology and opted for the latest version of his low-charge centralized ammonia system

The primary motivation Lepschat had for using CO₂over ammonia is CO₂’s relative safety. CO₂ has been used for decades in breweries, soft drink plants and other industrial settings, yet “I would be hard-pressed to find cases in an industrial setting of fatalities from CO₂,” he said. “It’s not non-toxic, but it’s not nearly as toxic as ammonia.”

In an enclosed area, where there is the potential for asphyxiation from CO₂, “you start to feel crummy and get a headache before it reaches a toxic level,” he said. “So it is a little bit self-alarming.” In any event, industrial areas tend to be too large to allow for that scenario, he added.

Lepschat also cites the opportunity a transcritical system affords to eliminate the regulatory burdens imposed on users of ammonia systems; “If you can avoid the cost and exposure to great liability from fines, why not?”

But CO₂still had to pass muster as a practical and economical refrigeration system before Lepchat could support investing in it. Most importantly, he had to answer the question, “Is there any one thing that’s going to make us say no?” he noted at the ATMOsphere America conference in June (organised by R744.com publisher shecco).

Lepschat first weighed transcritical CO₂ against other refrigeration options, such as the kind of low-charge central ammonia system he has installed over the past several years, low-charge packaged units, and even a packaged HFC unit.

He quickly eliminated the HFC unit because of the uncertainty surrounding its regulation due to HFCs’ high GWP, its “brutal” energy performance and the high cost of HFCs ($30/lb). He also dismissed packaged ammonia systems because of their cost, driven in part by the need for roof upgrades to support their weight.

That left low-charge central ammonia as the baseline for comparison to transcritical. In particular, Lepschat compared transcritical’s actual and sometimes projected costs to the costs associated with his low-charge ammonia central system in the Salem, Ore., plant that opened in 2017, which is similar in size and scope to the Grandview facility.

Next March at the IIAR Natural Refrigeration Conference & Expo in Phoenix, Lepschat plans to be part of a presentation comparing the costs of the Grandview facility’s CO₂ system with those of the baseline low-charge ammonia central system in Salem.

Energy savings with CO₂

Among the key metrics that Lepschat analyzed were reliability (no late night calls that the system is down) and energy use, for which he could make projections. “These are the cornerstones of our business,” he said.

Lepschat hired Energy350, Portland, Ore., to compare the energy consumption per hour of every component of the transcritical system and the baseline system for a given TR. The company projected there would be an electricity savings of 46,000 kWh/yr. Energy350 “has been amazingly accurate in the past with our ammonia plants,” he said. “So I expect similar results.”

Lepschat employs the cold-storage industry’s energy consumption metric, which is kW/cu ft/yr. Henningsen’s average across its warehouses is 0.4 (ranging from 1.1 to .27), compared to the IARW industry average of 1.21. “Energy efficiency is a big one for us,” said Lepschat. “We’ve done a good job managing that.”

Because of its projected energy efficiency, the transcritical system at Grandview earned a $262,000 energy incentive from a local utility (Pacific Power), which helped “level the playing field” for the CO₂ system, said Lepschat. (It was not included in his cost comparison.)

It is well known that the ambient climate affects a transcritical CO₂ system’s energy efficiency. Notably, warm climates in the 80°F-90°F range complicate the condensation of CO₂, increasing the system’s energy usage. While Grandview, Wash., has a moderate climate, its summers can be quite hot, as was the case this year.

But Lepschat gained confidence in transcritical’s efficiency in warmer ambient temperatures from a presentation about “using CO₂ with ammonia-type equipment,” given by Australian engineer Klaas Visser at an IIAR conference. “He showed that the continental U.S. – save for South Florida – is a viable place for CO₂,” he said. Visser was among the “impartial” people “who helped me to justify this,” he added.

So far, the Grandview system has been operating mostly during high-temperature months (June-September), which were “extraordinarily hot months up there,” said Lepschat. “The expectation is that when it’s very hot, CO₂ will pay an energy penalty, but it more than makes up for that penalty during the off-season.”

Even during the hot period, the adiabatic condenser prevents the system from entering less-efficient transcritical mode for all but “a few hours,” said Lepschat. “Anytime it’s over 75°F outside, you need the adiabatic system to keep the condensing temperature subcritical. When it’s 90°F outside, the condenser thinks it’s 62°F.”

In Grandview, the adiabatic process is helped by the dryness of the air. “It’s semi-arid; sagebrush grows there,” he said.

Because the transcritical system’s energy savings is driven by the use of the adiabatic condenser, Lepschat opted for adiabatic rather than use a less expensive air-cooled condenser. “We wanted the system to operate as efficiently as possible,” he said. “We were willing to pay extra for measures that will improve efficiency.” He expects the greater efficiency to result in an ROI on the premium and “lifecycle savings.”

He relied on the engineering expertise of Carnot in deciding not to purchase other energy-saving technology for the transcritical system, such as an ejector or parallel compression.

Lepschat will also reduce overall building energy costs by leveraging the CO₂ system’s considerable heat from discharge gas. It will be used to warm the floor under the freezer and to minimize defrost in the freezer by getting rid of moisture in the dock area (preventing it from entering the freezer). He estimates that up to 90% of the load in the freezer is due to warm moist air infiltrating the freezer room and creating ice that needs to be defrosted.

“You still have to defrost, but it’s a lot less often,” he said. The system defrosts with hot gas.

Other savings

Energy is not the only area where Lepchst sees savings. The installed cost of the transcritical system was $534,000 less than that of the baseline system; this included the savings gained from not building a machine room, which ranged between $200,000 and $400,000.

Not having a machine room was also a time saver; an engine room takes six weeks to build while the transcritical system was built at Carnot Refrigeration's factory and installed in three hours.

Another plus for the transcritical system is that its evaporators hang in the same spot in the freezer room where ammonia evaporators hang in other buildings. “So structurally, there was no modification to the freezer box, which was familiar to us,” he said.

In anticipation of taking on more cold storage business, Lepschat left space for one more evaporator and two more compressors, gaining another 32 TR for the freezer that would be used to freeze product (the other freezer space is for storage). Henningsen did get the additional business, and the equipment was installed.

In addition, Lepschat decided to create another area within the existing facility where a second compressor rack/condenser system, supporting six more evaporators, could be installed to support additional business. Alternatively, Henningsen may decide to invest in a new adjoining building with its own transcritical system.

There are a number of changes in material and techniques that Lepschat had to make in transitioning from ammonia to CO₂. “You don’t do things because you did it that way with ammonia,” said Lepschat. “It might not be cost-effective, and it might be flat wrong.”

For example, with the CO₂ system Lepschat employed corrosion-resistant stainless steel tubing in all suction and liquid lines connecting evaporators in the freezer and dock to the compressor rack and condenser/gas cooler, respectively. By contrast, he used arc-welded carbon-steel piping in the low-charge ammonia system.

The stainless steel tubing is welded via machine-operated orbital welding, which is new for Henningsen and “a lot of people in the industry,” said Lepschat.

While Henningsen’s contractor, PermaCold Engineering, is familiar with orbital welding, this was the contractor’s first field experience with the technique. “They learned how to do it outside,” Lepschat said.

This is an example, he said, of PermaCold’s willingness to “step out of the box” and work with a new technology. “You’ve got to find a contractor willing to do that; many are not.”

Lepschat was able to limit the length of outside suction tubing to the compressor; the rest was inside the freezer with the evaporators. “That saved us on construction costs” and lessened welding done outside, he noted.

With the stainless steel tubing, he is also able to use Armaflex insulation, which is not possible with carbon steel. Armaflex is less expensive and easier to install, he said.

By using an adiabatic condenser rather than an evaporative condenser, Henningsen substantially reduces its water and sewer costs, noted Lepschat. “For the bulk of the year – fall, winter and spring – it will run without water,” he said.

Going to school on CO₂

Another essential element for transitioning to new technology is training. Carnot Refrigeraton came to Grandview on two occasions – with more to come – to train technicians, both PermaCold’s and his own. In addition, Lepschat has started sending Henningsen’s technician to CO₂ classes at the Industrial Refrigeration Training Center (IRTC) in Lyndhurst, Va.

“We’re going to all go to school together,” said Lepschat. “My guys and my service company are going to get educated.”

The training in all cases emphasizes “conceptual knowledge,” he said. “We teach how it works because if they understand the theory of what’s going on inside the pipes, they are much more effective in figuring out when something’s not going right.”

Some of the key issues technicians face in CO₂ systems are high pressures and the potential to form dry ice. “I’m satisfied in my mind there’s no danger from pressure because of the system we installed and because of pressure testing,” he said. “And the odds of dry ice in pipes are slim if you take the correct precautions and have the right training.”

To ease the first-year learning period for Henningsen, Carnot monitors the system remotely from its Quebec headquarters on a 24X7 basis, using sophisticated technology, and oversees any required maintenance. “It’s like NASA,” said Lepschat. But when the one-year warranty expires, “we take that on ourselves,” he noted.

Ultimately, once technicians are up to speed, he expects transcritical CO₂ to need less maintenance than central ammonia systems, which require many regulation-related and other activities that are not applicable to CO₂.

After some initial commissioning hiccups, the transcritical system has been “chugging along,” said Lepschat. “It’s not a dramatic system. It’s almost boring to watch. You can stand next to it and have a conversation.”

So far Lepschat’s biggest challenge is the newness of the system. “We’ve never done it before,” he said. “But we hadn’t done a lot of things before we did them the first time.”

For complete coverage of Henningsen Cold Storage's Grandview and Scranton CO₂ facilities, see the cover story in the October 2018 issue of Accelerate America.